Enamels and enamelling; an introduction to the preparation and ...

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SUBSIDIARY MATERIALS. 89
a faint one the amount of iron is so small as to be
practically negligible, so far as its influence on the colour of
enamel is concerned. On the other hand, if a deep coloration
is produced, or a blue precipitate is formed, the water must
be regarded as highly ferruginous and likely to contain iron
sufficient to spoil the beauty of delicate coloured enamels.
The presence of comparatively large quantities of iron can
also be recognised by the formation of a flocculent brownish
precipitation of ferric hydrate when the water is boiled. The
lime and magnesia salts and sodium chloride, almost invariably
present in well and spring water, are unimportant for our
purpose.
It is evident from the foregoing that the manufacturer of
enamels should endeavour to obtain perfectly clear water, free
from sulphuretted hydrogen or any appreciable quantities of
iron compounds. When the water is intended for use in the
materials it is essential
preparation of certain pure pigmentary
to employ nothing but distilled, or very pure well water.
FUEL.
In the enamel industry very large quantities of fuel are
consumed, it being necessary to heat the masses to high
temperatures in order to bring them into a state of fusion
In this connection not only is the cost of the fuel in relation
to its calorific power a matter of some importance, but also
the indirect influence the fuel may exert on the quality of the
eiiamel mass should be considered. For example, when a fuel
yields a large quantity of specifically light ash, it may happen
that some of the latter gains access to the enamel mass and
affects its colour. Wood ashes always contain small amounts
of unconsumed carbon (hence their grey colour), and should
a small quantity of this ash find its way into an enamel mass
containing no oxidising materials, the upper layers of the
mass would acquire a decided grey tinge. Still more injurious